MF & HF-SSB Duplex Channels

We have already covered the recognized MF/HF Simplex Frequencies and their importance in ship to ship and distress communications. Here we will concentrate on the HF - Duplex Channels used in typical ship to shore communications.

In its simplest terms, a Duplex Channel is simply (2) different simplex frequencies paired together to form a channel. (1) frequency is used to transmit and the other is used to receive. As an example, If you select ITU Channel 401 on your HF-SSB to communicate on your radio, you will be transmitting on 4065.0 kHz and receiving on 4357.0 kHz.

MF/HF-SSB Page Menu

It is important to note that Marine HF-SSB radios (much like the Marine VHF,) are not true duplex radios, but better described as "half-duplex." This means that the radio can only be in one of two states: either a transmitter or a receiver, it cannot be in both states simultaneously unless you have special equipment installed along with your radio. Most radios are toggled between these two states (transmit and receive) by the push to talk button. This however does not change the fact that the use of different paired frequencies are known as duplex channels.

Are there any advantages to the use of duplex channels? Surprisingly, very few. However, these advantages are major from the perspective of a coast station. They allow for "repeater" usage; which often extends the range of communications by allowing more transmit power to be used and also allows for the ability to locate the antenna in a more advantageous location. This being the typical reasoning behind the usage of duplex channels in ship to shore communications.

Frequency Bands

Like the simplex frequencies, the HF Marine SSB duplex frequencies are grouped into frequency bands. There are currently 9 bands that have been allocated for marine service:

2 MHz

4 MHz

6 MHz

8 MHz

12 MHz

16 MHz

18 MHz

22 MHz

25 MHz

We will ignore the 2 MHZ frequencies, due to their limited range, leaving us with 8 frequency bands that most duplex channels fall into.

HF Duplex Channel Pairs

In the dropdowns below, we have provided a complete list of all internationally accepted ITU standard frequency pairs. These frequency pairs have been broken down by their frequency bands and identified by their channel number.

In your typical marine HF-SSB radio a large number of these channels are pre-programed into the set by the manufacturer. They also have memory space available to allow the user to enter others.

ITU 4 MHz Channels

4 MHz Duplex Channel Frequency Pairs

ITU Channel No.

Coast Transmit / Ship Receive

Ship Transmit / Coast Receive

401

4357.0 kHz

4065.0 kHz

402

4360.0 kHz

4068.0 kHz

403

4363.0 kHz

4071.0 kHz

404

4366.0 kHz

4074.0 kHz

405

4369.0 kHz

4077.0 kHz

406

4372.0 kHz

4080.0 kHz

407

4375.0 kHz

4083.0 kHz

408

4378.0 kHz

4086.0 kHz

409

4381.0 kHz

4089.0 kHz

410

4384.0 kHz

4092.0 kHz

411

4387.0 kHz

4095.0 kHz

412

4390.0 kHz

4098.0 kHz

413

4393.0 kHz

4101.0 kHz

414

4396.0 kHz

4104.0 kHz

415

4399.0 kHz

4107.0 kHz

416

4402.0 kHz

4110.0 kHz

417

4405.0 kHz

4113.0 kHz

418

4408.0 kHz

4116.0 kHz

419

4411.0 kHz

4119.0 kHz

420

4414.0 kHz

4122.0 kHz

*421

4417.0 kHz

4125.0 kHz

422

4420.0 kHz

4128.0 kHz

423

4423.0 kHz

4131.0 kHz

424

4426.0 kHz

4134.0 kHz

425

4429.0 kHz

4137.0 kHz

426

4432.0 kHz

4140.0 kHz

427

4435.0 kHz

4143.0 kHz

428

4351.0 kHz

(Varies)

429

4354.0 kHz

(Varies)

*This channel is not recommended due to the use of the 4 MHz Distress, Safety, & Calling frequency within the channel pair.

ITU 6 MHz Channels

6 MHz Duplex Channel Frequency Pairs

ITU Channel No.

Coast Transmit / Ship Receive

Ship Transmit / Coast Receive

601

6501.0 kHz

6200.0 kHz

602

6504.0 kHz

6203.0 kHz

603

6507.0 kHz

6206.0 kHz

604

6510.0 kHz

6209.0 kHz

605

6513.0 kHz

6212.0 kHz

*606

6516.0 kHz

6215.0 kHz

607

6519.0 kHz

6218.0 kHz

608

6522.0 kHz

6221.0 kHz

*This channel is not recommended due to the use of the 6 MHz Distress, Safety, & Calling frequency within the channel pair.

ITU 8 MHz Channels

8 MHz Duplex Channel Frequency Pairs

ITU Channel No.

Coast Transmit / Ship Receive

Ship Transmit / Coast Receive

801

8719.0 kHz

8195.0 kHz

802

8722.0 kHz

8198.0 kHz

803

8725.0 kHz

8201.0 kHz

804

8728.0 kHz

8204.0 kHz

805

8731.0 kHz

8207.0 kHz

806

8734.0 kHz

8210.0 kHz

807

8737.0 kHz

8213.0 kHz

808

8740.0 kHz

8216.0 kHz

809

8743.0 kHz

8219.0 kHz

810

8746.0 kHz

8222.0 kHz

811

8749.0 kHz

8225.0 kHz

812

8752.0 kHz

8228.0 kHz

813

8755.0 kHz

8231.0 kHz

814

8758.0 kHz

8234.0 kHz

815

8761.0 kHz

8237.0 kHz

816

8764.0 kHz

8240.0 kHz

817

8767.0 kHz

8243.0 kHz

818

8770.0 kHz

8246.0 kHz

819

8773.0 kHz

8249.0 kHz

820

8776.0 kHz

8252.0 kHz

821

8779.0 kHz

8255.0 kHz

822

8782.0 kHz

8258.0 kHz

823

8785.0 kHz

8261.0 kHz

824

8788.0 kHz

8264.0 kHz

825

8791.0 kHz

8267.0 kHz

826

8794.0 kHz

8270.0 kHz

827

8797.0 kHz

8273.0 kHz

828

8800.0 kHz

8276.0 kHz

829

8803.0 kHz

8279.0 kHz

830

8806.0 kHz

8282.0 kHz

831

8809.0 kHz

8285.0 kHz

832

8812.0 kHz

8288.0 kHz

*833

8291.0 kHz

8291.0 kHz

834

8707.0 kHz

(Varies)

835

8710.0 kHz

(Varies)

836

8713.0 kHz

(Varies)

837

8716.0 kHz

(Varies)

*This channel is not recommended due to the use of the 8 MHz Distress, Safety, & Calling frequency within the channel pair.

ITU 12 MHz Channels

12 MHz Duplex Channel Frequency Pairs

ITU Channel No.

Coast Transmit / Ship Receive

Ship Transmit / Coast Receive

1201

13,077.0 kHz

12,230.0 kHz

1202

13,080.0 kHz

12,233.0 kHz

1203

13,083.0 kHz

12,236.0 kHz

1204

13,086.0 kHz

12,239.0 kHz

1205

13,089.0 kHz

12,242.0 kHz

1206

13,092.0 kHz

12,245.0 kHz

1207

13,095.0 kHz

12,248.0 kHz

1208

13,098.0 kHz

12,251.0 kHz

1209

13,101.0 kHz

12,254.0 kHz

1210

13,104.0 kHz

12,257.0 kHz

1211

13,107.0 kHz

12,260.0 kHz

1212

13,110.0 kHz

12,263.0 kHz

1213

13,113.0 kHz

12,266.0 kHz

1214

13,116.0 kHz

12,269.0 kHz

1215

13,119.0 kHz

12,272.0 kHz

1216

13,122.0 kHz

12,275.0 kHz

1217

13,125.0 kHz

12,278.0 kHz

1218

13,128.0 kHz

12,281.0 kHz

1219

13,131.0 kHz

12,284.0 kHz

1220

13,134.0 kHz

12,287.0 kHz

*1221

13,137.0 kHz

12,290.0 kHz

1222

13,140.0 kHz

12,293.0 kHz

1223

13,143.0 kHz

12,296.0 kHz

1224

13,146.0 kHz

12,299.0 kHz

1225

13,149.0 kHz

12,302.0 kHz

1226

13,152.0 kHz

12,305.0 kHz

1227

13,155.0 kHz

12,308.0 kHz

1228

13,158.0 kHz

12,311.0 kHz

1229

13,161.0 kHz

12,314.0 kHz

1230

13,164.0 kHz

12,317.0 kHz

1231

13,167.0 kHz

12,320.0 kHz

1232

13,170.0 kHz

12,323.0 kHz

1233

13,173.0 kHz

12,326.0 kHz

1234

13,176.0 kHz

12,329.0 kHz

1235

13,179.0 kHz

12,332.0 kHz

1236

13,182.0 kHz

12,335.0 kHz

1237

13,185.0 kHz

12,338.0 kHz

1238

13,188.0 kHz

12,341.0 kHz

1239

13,191.0 kHz

12,344.0 kHz

1240

13,194.0 kHz

12,347.0 kHz

1241

13,197.0 kHz

12,350.0 kHz

*This channel is not recommended due to the use of the 12 MHz Distress, Safety, & Calling frequency within the channel pair.

ITU 16 MHz Channels

16 MHz Duplex Channel Frequency Pairs

ITU Channel No.

Coast Transmit / Ship Receive

Ship Transmit / Coast Receive

1601

17,242.0 kHz

16,360.0 kHz

1602

17,245.0 kHz

16,363.0 kHz

1603

17,248.0 kHz

16,366.0 kHz

1604

17,251.0 kHz

16,369.0 kHz

1605

17,254.0 kHz

16,372.0 kHz

1606

17,257.0 kHz

16,375.0 kHz

1607

17,260.0 kHz

16,378.0 kHz

1608

17,263.0 kHz

16,381.0 kHz

1609

17,266.0 kHz

16,384.0 kHz

1610

17,269.0 kHz

16,387.0 kHz

1611

17,272.0 kHz

16,390.0 kHz

1612

17,275.0 kHz

16,393.0 kHz

1613

17,278.0 kHz

16,396.0 kHz

1614

17,281.0 kHz

16,399.0 kHz

1615

17,284.0 kHz

16,402.0 kHz

1616

17,287.0 kHz

16,405.0 kHz

1617

17,290.0 kHz

16,408.0 kHz

1618

17,293.0 kHz

16,411.0 kHz

1619

17,296.0 kHz

16,414.0 kHz

1620

17,299.0 kHz

16,417.0 kHz

*1621

17,302.0 kHz

16,420.0 kHz

1622

17,305.0 kHz

16,423.0 kHz

1623

17,308.0 kHz

16,426.0 kHz

1624

17,311.0 kHz

16,429.0 kHz

1625

17,314.0 kHz

16,432.0 kHz

1626

17,317.0 kHz

16,435.0 kHz

1627

17,320.0 kHz

16,438.0 kHz

1628

17,323.0 kHz

16,441.0 kHz

1629

17,326.0 kHz

16,444.0 kHz

1630

17,329.0 kHz

16,447.0 kHz

1631

17,332.0 kHz

16,450.0 kHz

1632

17,335.0 kHz

16,453.0 kHz

1633

17,338.0 kHz

16,456.0 kHz

1634

17,341.0 kHz

16,459.0 kHz

1635

17,344.0 kHz

16,462.0 kHz

1636

17,347.0 kHz

16,465.0 kHz

1637

17,350.0 kHz

16,468.0 kHz

1638

17,353.0 kHz

16,471.0 kHz

1639

17,356.0 kHz

16,474.0 kHz

1640

17,359.0 kHz

16,477.0 kHz

1641

17,362.0 kHz

16,480.0 kHz

1642

17,365.0 kHz

16,483.0 kHz

1643

17,368.0 kHz

16,486.0 kHz

1644

17,371.0 kHz

16,489.0 kHz

1645

17,374.0 kHz

16,492.0 kHz

1646

17,377.0 kHz

16,495.0 kHz

1647

17,380.0 kHz

16,498.0 kHz

1648

17,383.0 kHz

16,501.0 kHz

1649

17,386.0 kHz

16,504.0 kHz

1650

17,389.0 kHz

16,507.0 kHz

1651

17,392.0 kHz

16,510.0 kHz

1652

17,395.0 kHz

16,513.0 kHz

1653

17,398.0 kHz

16,516.0 kHz

1654

17,401.0 kHz

16,519.0 kHz

1655

17,404.0 kHz

16,522.0 kHz

1656

17,407.0 kHz

16,525.0 kHz

*This channel is not recommended due to the use of the 16 MHz Distress, Safety, & Calling frequency within the channel pair.